JPH03122616A - Driving method for ferroelectric liquid crystal element - Google Patents

Abstract

PURPOSE:To accurately reproduce continuous gradations even by time-division driving by providing three table states together and modulating the product of the crest value and pulse width of a voltage applied to the ferroelectric liquid crystal element. CONSTITUTION:Chiral smectic ferroelectric liquid crystal 15 is sandwiched between two glass substrates 11 and 12 where oblique vapor-deposited orienting films 14 of inorganic insulators which have mutually opposite slanting directions are stuck and the thickness is set to 1.5 - 4 microns. Then, three kinds of states, i.e. 1st state wherein liquid crystal molecules are nearly parallel to the substrates 11 and 12 and slant to the right from the molecule layer normal, 2nd state wherein the liquid crystal molecules slant to the left from the layer normal, and 3rd state wherein the molecules are in twist structure while differing in angle to the layer normal on the opposite substrates are provided together as sufficiently stable states. For a half-tone display, >=2 of the stable states are required, but half-tones vary continuously according to variation in value prescribed by the product of the crest value and pulse width of the applied voltage with a voltage waveform. Consequently, the continuous half-tones can accurately be displayed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal element having a ferroelectric liquid crystal as a liquid crystal layer, in which the amount of transmitted light can be controlled in continuous gradations.

[Conventional technology and its issues]

Because ferroelectric liquid crystal elements have memory properties and high-speed response on the microsecond scale, they are expected to be put to practical use in large-capacity displays and high-speed liquid crystal shutters.

By the way, when putting a ferroelectric liquid crystal element into practical use, there is a technical problem in continuous gradation control of the amount of transmitted light during time-division driving. For example, in Japanese Patent Application Laid-Open No. 62-160420, there is an example in which gradation display is attempted during time-division driving using three states: two uniform liquid crystal alignment states and a twisted liquid crystal alignment state. Only the scale is displayed. Furthermore, Japanese Patent Application Laid-open No. 59-193427 has an example in which multi-gradation display is attempted by mixing bistable states by changing the number of drive pulses, but according to the author's experiments, half-tone display is attempted during time-division driving. The level changed over time, making it impossible to obtain stable halftone display.

Therefore, it is an object of the present invention to provide a method for driving a ferroelectric liquid crystal element that can accurately reproduce continuous gray levels even when driven in a time-division manner.

[Means to solve the problem]

In order to achieve the above object, an alignment film of an inorganic insulator is formed on the opposing surfaces of a pair of substrates of a ferroelectric liquid crystal element by oblique evaporation, the film being inclined with respect to each surface and the directions of inclination being opposite to each other. , the thickness of the chiral smectic ferroelectric liquid crystal between the substrates is set between 1.5 and 4 microns, and a first state (first state) in which the liquid crystal molecules are approximately parallel to the substrates and tilted to the right from the molecular layer normal is established. 1 uniform state), a second state tilted to the left from the molecular layer normal (second uniform state), and a third state in which the molecules form a twisted structure with different angles with the layer normal on the opposing substrate. The three types of states (twisted state) are mixed so that each shows a sufficiently stable state,
It is characterized by applying a voltage waveform that modulates the product of voltage peak value and pulse width to a ferroelectric liquid crystal element to display continuous gradation.

[Effect]

The operation of the present invention will be explained below based on the drawings.

Figure 4 shows three liquid crystal alignment states of a liquid crystal device in which a chiral smectic ferroelectric liquid crystal is sandwiched between two glass substrates to which obliquely vapor-deposited alignment films of inorganic insulators are attached, the tilt directions being opposite to each other. and the driving voltage waveform that selects each of those states,
The transmittance T of each state is shown in correspondence with the wavelength of transmitted light (0), where (a) and (b) are the uniform state, and (C) is the twisted state. Here, the molecules 41 and 42 in the orientation state column are in the fourth positive 4L 42 molecular state.

On the other hand, in order to obtain a half-tone display, it is necessary to mix two or more stable states, but it is more likely to mix a twisted state and a uniform state (voltage waveform) than to mix two uniform states. The intermediate tone changes continuously according to the change in the value defined by the product of the high value and the pulse width.Therefore, for intermediate tone display, a ferroelectric liquid crystal element that is stable in both the uniform state and the twisted state is required. By the way, the stability of states (a), (b), and (C) in Fig. 4 differs depending on the liquid crystal layer thickness.In other words, when the liquid crystal layer thickness is 4μ or more, only the stability of state (C) increases; The two states (a) and (b) rarely appear and show a monostable state.On the contrary, in a liquid crystal layer thickness of 1.5μ or less, (a)
), (b) state selection voltage asymmetry appears, (
C) The state may become unstable. As a result, a ferroelectric liquid crystal device having a liquid crystal layer thickness of 1.5 μm to 4 μm exhibits three stable states in which both the uniform state and the twisted state are stabilized, and becomes a liquid crystal device capable of displaying halftones.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a schematic cross-sectional view of a ferroelectric liquid crystal device showing an embodiment of the present invention, in which two glass substrates 11 and 120 with transparent electrodes 13 attached thereto, and an alignment film 14 deposited obliquely on the opposing surfaces of the glass substrates 120.
Two glass substrates are arranged so that the glass substrates adhere to each other and are tilted oppositely to each other, and a liquid crystal C8-101 manufactured by Chisso Corporation is placed in a gap of 24 microns surrounded by an epoxy resin seal 16.
4 are sandwiched together to form a ferroelectric liquid crystal element. Polarizing plates 17 and 18 in a crossed Nicol state are arranged on the upper and lower surfaces of the liquid crystal element, respectively, and a resistance heater 1 is arranged on the liquid crystal element.
9 was installed to maintain the device at a constant temperature.

The element temperature is 1 below the chiral smectic phase transition temperature.
It was set at around 5 degrees. The reason for this is that when the test time-division drive waveform of the selection voltage ±vo shown in Figure 5(a) is applied, fluctuations in the stable state as shown in (b) due to the non-selection voltage of ±1/3V0 occur. This is because, as shown in (C), the minimum driving temperature T- is in the range of 10 degrees to 20 degrees below the phase transition temperature.

Under the liquid crystal element configuration and driving temperature described above,
Vo
The test was carried out under conditions of IOV and pulse width of 60 μs. Third
The figure shows the operating characteristics of the ferroelectric liquid crystal element during the time-division driving described above, in which (a) shows the drive voltage waveform and (1) shows the intensity of transmitted light. 61 is a voltage waveform during the selection period, and 62 to 64 in (b) are extracted voltage waveforms of different gradations. With this driving method, accurate intermediate tones can be achieved with a contrast ratio of 1 to 1 between the black level and the white level.
Obtained within 120 minutes. Note that even when using a liquid crystal element using ferroelectric liquid crystals FeJix005 and pelixo09 manufactured by Hoechst, accurate halftone display was similarly obtained.

〔Effect of the invention〕

As described in the above embodiments, according to the present invention, by mixing three stable states, it is possible to provide a ferroelectric liquid crystal element that accurately displays continuous halftones.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of the ferroelectric liquid crystal element of the present invention, and FIG.
The figure is an explanatory diagram showing the time-division driving waveform of the present invention, FIG. 3 is an explanatory diagram showing the optical response of a ferroelectric liquid crystal element during time-division driving, and FIGS. A schematic explanatory diagram showing three states of a liquid crystal element, Figure 5 (O) is a schematic waveform diagram showing fluctuations in the stable state of a ferroelectric liquid crystal element during time-division driving. 1.12... ... Glass substrate, 6 ... Transparent electrode, 4 ... SiO oblique evaporation film, 5 ... Liquid crystal layer, 6 ... Epoxy resin seal, 7 .18...Polarizing plate. Figure 2 (31 Figure 4 (A)

Claims (2)

[Claims] (1) A chiral smectic ferroelectric liquid crystal is sandwiched between a pair of substrates having electrodes on opposing surfaces, and a first stable state in which the molecules are approximately parallel to the substrates and tilted to the right from the molecular layer normal; Ferroelectricity exhibits gradation through a second stable state in which the molecules are parallel and tilted to the left from the layer normal, and a third stable state in which the molecules form a twisted structure with different angles with the layer normal on the opposing substrate. In the method for driving a liquid crystal element, the above three stable states are mixed, and the three stable states are mixed, and the product of the voltage peak value and pulse width applied to the ferroelectric liquid crystal element is modulated.
A method for driving a ferroelectric liquid crystal device characterized by changing the ratio of a mixture of two stable states and displaying continuous gradations. (2) A method of coexisting the three stable states is to form alignment films of inorganic insulators on opposing surfaces of the pair of substrates by oblique evaporation, which are inclined with respect to each surface and whose directions of inclination are opposite to each other. At the same time, the thickness of the liquid crystal layer between the substrates was increased from 1.5μ to 4μ.
2. The method of driving a ferroelectric liquid crystal element according to claim 1, wherein the driving method is set between μ.